Phenotypic trait variation in genetically distincts Arabidopsis thaliana populations from the Pyrenees Mountains highlight acclimation to environmental constraints.

International audienceThe natural diversity is a free reservoir of variation for studying morphological and developmental traits. Studying natural variation will help to identify genetic mechanisms of complex traits. Mountain habitats provide genuine environmental temperature gradients where plants need to adapt to multiple environments. In this study, we report the identification and genetic study of 341 individuals of Arabidopsis thaliana (representing 30 new natural populations), collected between 200 and 1800 m above sea level in the Pyrenees Mountains that constitute a physical barrier between Spain and France. We used class III peroxidases (CIII Prx) gene sequences as polymorphic markers to evaluate their genetic variation in nature and determine the genetic relationships between populations along a altitudinal gradient in the Pyrenees. Using Bayesian-based statistics and molecular phylogenetic analyses, we proved that a genetic cluster from the Pyrenees Mountains appears with clear demarcation from any other known ecotypes. Then we demonstrated that the individuals are genetically separated in two major clusters and some homogeneous populations are found. These populations exhibited also great phenotypic variability (e.g. germination speed, chlorophyll content, height…) when intentionally grown at sub-optimal temperature (22°C vs 15°C) to mimic natural environment. Finally, we provide evidence that this genetic variation is also expressed with natural intraspecific morphological variations. Therefore this study sheds a new light regarding the west European population structure and phenotypic plasticity of A. thaliana at contrasted temperatures, and illustrates the fact that integrative analysis combining genetic, phenotypic and climatology variation is a powerful tool for predicting acclimation of population in a global warming context. These new Pyrenean populations are made available to the scientific community and represent a new tool of choice for studying cold tolerance and development